Attentional deficit appears to be a core problem in many clinical disorders including childhood autism, schizophrenia, mental retardation, and psychopathy. The objectives of the proposed research are to understand, in normal young adults, the role played by voluntary and automatic orienting/attentional systems in controlling how information is processed. The method employed will probe information processing by means of the modulation of three reflexes, mediated at different levels of the nervous system -- heart rate, startle blink, and the "prepulse inhibition" of blink. The latter is a relatively low-level effect which depends on a transient change in stimulation occurring shortly before a reflex-eliciting probe. The methods have the advantage of being useful across the life span and with otherwise inaccessible patient populations. An important question in information processing is how early in processing attentional control can have an influence in enhancing or selecting some forms of stimulation and attenuating others. The proposed research would determine whether or not blink modulation effects which suggest an early influence could be explained either as receptor-adjusting effects or as late post-perceptual effects. A receptor-adjusting explanation will be tested by 1) assessing differences in attentional modulation of an early oligosynaptic and a late polysynaptic component of the cutaneous blink reflex and 2) determining whether inputs which overlap peripherally are nonetheless processed differently. A late selection explanation will be tested by determining whether attention to novelty or semantic category modulates blinks elicited by such stimuli or only blinks elicited by subsequent probes. An upper limit for the time to detect mismatch would be estimated. The question of how post-perceptual processing affects receptivity to further sensory intake and readiness for motor output is also important. Opposed predictions, based on assumptions concerning the relation of heart rate change to motor excitation, will be tested by measuring blink modulation when attention is directed to manipulation of stimulus images or codes.